Recent form suggests this could be the most competitive quarterfinal of the day, as both women have roared through week one without surrendering a set.

In fact, a stingy Radwanska has not dropped a set all season, including a 6-3, 6-4 sweep of Li in Sydney a few weeks ago. Watching the 123-pound Radwanska defuse heavier hitters is like watching a woman armed with a paint brush win a joust against an opponent wielding a 2x4. The clever Pole can play all-court tennis when she chooses, or rely on her shrewd court sense, soft hands, and flair for finesse to redirect opponents to obscure areas.

Former French Open champion Li has more firepower. The Pole plays off pace effectively, especially off her versatile two-handed backhand, which is her kill shot. But I believe the faster court favors Li: She is the more explosive player and her serve is more lethal—when she’s landing it.

Li has won four of their five hard-court clashes, they split their two prior major matches at Wimbledon, and the fact that both are very quick around the court should make for entertaining rallies. This could be a tight test, but if she stays calm and maintains the right balance between aggression and control, I like Li to advance to her third Aussie Open semifinal in the past four years.

These two Russians have a history together, and it doesn’t evoke many positive memories for Makarova. The reigning French Open champion has dominated this rivalry, winning eight of nine sets and sweeping all four sets they’ve played on hard courts, including a routine, 6-2, 6-3, win in last year's Aussie Open quarterfinals.

The good news for Makarova is when she’s landing her hooking lefty serve that sets up her first strike, she can beat anyone—she handed a hobbled Serena Williams one of her most lopsided major losses here last year, and she swept Angelique Kerber in the fourth round. The bad news is that Sharapova has been so scary ripping her returns that even if you hit the corners of the service box, it can open up a sharper angle for a vicious return blast. The 2008 champion has won 23 of 27 return games.

Tearing through the field with a ruthlessness usually only found in MMA fighters, Sharapova has permitted just five games in four tournament wins, force-feeding five bagels along the way. She has been crushing the first strike with conviction and controlling the middle of the court; and once she has you playing defense, it’s very tough to get off that treadmill. While I don’t discount Makarova, Sharapova is so strong right now she looks to be on a fast track to the final that I don’t see her making a mis-step here.

This is a milestone match for Ferrer, but it’s been a horror show for Almagro. Ferrer is bidding for his 500th career victory and second trip to the Aussie Open semifinals, while Almagro tries to halt a humbling history. He has played more pro matches against Ferrer than any other player—and lost more matches to Ferrer than anyone else.

A clean, beautiful ball striker, Almagro has minimized the mood swings that have plagued him in the past, but still must be haunted by the sight of Ferrer on the other side of the net. Contesting his fifth consecutive major quarterfinal, Ferrer’s quickness and court positioning—he plays closer to the baseline and often beats Almagro to the punch—give him the advantage.

Auckland champion Ferrer is on an 11-1 roll this season and hasn’t lost to a Spanish man other than Rafael Nadal since 2010. He has strengthened his serve considerably since his early days on the tour and he can create acute angles with his forehand. Look for Ferrer to play some shorter angles to exploit Almagro’s deeper court positioning and aversion to the net.

Playing for his first major semifinal, Almagro will need an imposing serving day to threaten—he has 68 aces and is winning 82 percent of his first-serve points through four rounds. But the ferocious David has been a Goliath in this match-up, and I see him advancing to his fifth major semifinal.

There is a time and place for everything, but facing Djokovic anytime on a hard court has not been the time or place for Berdych.

Djokovic has downsized the big-hitting Czech in winning all 10 of their hard-court clashes, including a straight-sets thrashing in the 2011 Aussie Open quarterfinals. Berdych’s sheer power and suffocating flat, baseline blasts can spike stress levels of many opponents, but Djokovic isn’t one of them.

This is a comfortable match-up for Djokovic because he’s the more agile, athletic player, is the game’s best returner and mover on hard courts, and his eye-popping defensive skills seem to shrink the court against the 6’5” Berdych, who has tried to squeeze shots into increasingly smaller spaces in past losses, often finding frustration instead.

That said, Stanislas Wawrinka entered the fourth round with a similar history of futility against Djokovic, but the Swiss served boldly, attacked the Serbian’s second serve relentlessly, and closed at net at times in testing the champion before bowing in a gripping five-setter.

Berdych is a dynamic player, but he builds points based on depth and pace. Because Berdych hits flatter, he doesn’t produce the angles Djokovic can. I think this is a more straightforward match for Djokovic, and while fatigue could be a factor, the three-time champion has bounced back from epics before.